Polymerization of isobutylene is known for a variety of temperature, solvent initiator and Lewis acid combinations. Initiation may be carried out from water or alkyl halide initiators. Many examples exist in the literature where water is known to be the source of initiation. One well known example is the BF.sub.3.H.sub.2 O catalyst. Other Lewis acids have also been used including Titanium tetrachloride (TiCl4), aluminum trichloride (AlCl.sub.3), aluminum tribromide (AlBr.sub.3), tin tetrachloride(SnCl.sub.4), iron trichloride (FeCl.sub.3), and alkylaluminum halides (R.sub.n AlX.sub.3-n ;n=0, 1 or 2). Examples of other co-initiators are found with similar frequency. From this wealth of data it can be concluded that molecular weights and yields of homopolymers, fall off upon increasing the polymerization temperature and reducing the polarity of the solvent. One of the best systems for preserving both yield and molecular weight at higher polymerization temperatures is that based on alkyl-aluminum halides. Even though alkyl-aluminum halide catalysts can be used in nonpolar solvents, the ability of the halide alone to cause initiation of isobutylene in addition to initiation from water or other added initiation sources creates a system which can generate polymers and copolymers of reasonably broad molecular weight distribution, i.e. Mw/Mn.gtoreq.4, especially with styrenic comonomers. Supported alkoxyaluminum halides have been used for the homopolymerization of isobutylene to molecular weights higher than those from other catalysts at similar temperatures (see T. C. Cheng, et al., in POLYMER BULLETIN 28, 123, 1992).
For an industrially applicable process these above catalysts and polymerization conditions fall short of commercial usefulness. Improvements in these systems would include elimination of boron and titanium based Lewis acids as they present handling and purification problems. Also a reduction in the amount of catalyst used would be desirable and a reduction in polymerization time would be desirable.
Polymerization processes that avoid the use of halogenated solvents are desirable from many perspectives. However, this restriction eliminates many Lewis acid systems from consideration because of their poor polymerization capabilities in nonpolar solvents. Alkyl aluminum halides can be used with non-polar solvents, but can lead to problems with MWD control and hence property control. An attractive system would be capable of providing copolymers of reasonably high molecular weight with good polydispersity control from a nonpolar polymerization solvent or a solvent system which minimized the amount of polar component required.